jfreechart terminology

[puck.of.pooks.hill]

hi,
i have a hard time figuring out what the terms used in the api actually mean.
is there some kind of document describing the available elements, names and their function (TickUnit? Category-/Item/BaseLabel? DomainAxis?? Chart types ...)?

current use case:
i got a database containing the number of logins. user wants a chart detailing the number of logins per hour -- for a period that may span from a day to a year.
it's pretty clear that for a year the labels on the x axis will form a illegible large block, so i want to print only a label for, say, a day not every single hour.

the code i inherited uses here a CategoryPlot -- for a similar use case i found the recommendation to use XYPlot. what's the difference here? what's a "category" in jfreechart speak?
since XYPlot apparently does not allow for a custom selection of labels to print (and label rotation apparently only is vertical or horzontal instead of CategoryPlot's free value) and switching between two different plots just to accomodate the changing resolution only adds more code to maintain w/o added value, i tried to create my own labels.

here i discovered that there are at least three different kinds of labels and even more generators which to my surprise in no configuration actually change the labels of the x axis ...

sometimes after seeing the effects of recent coding, names of elemnts suddenly made sense, sort of, but very often i am stunned by the arcane terminolgy and almost missing and seldom helpful descriptions in the docs.

so, to sum up:

where do i find a comprehensive description of the ideas behind jfreechart and the terms used to describe those ideas? (purchasing the book does not count. i am not going to spend 50 bucks just for that kind of basic information)